Decreased enzyme activities are observable in many enzymes when stored for a prolonged period of time.
TGase is an enzyme whose enzyme activity is decreased in a marked degree due, mainly, to oxygen when stored for a prolonged period of time. In consequence, a process in which an organic acid, an inorganic acid, a polyphenol, a thiol compound, a sugar alcohol and the like are used as additives has been developed with the aim of improving shelf life of TGase (cf. Japanese Patent Application Kokai No. 4-207194). However, improvement of shelf life by these additives is not sufficient. Especially, when TGase is stored under severe conditions such as storage throughout the summer season after its production, it is necessary to provide a proper means such as the use of an oxygen scavenger or vacuum treatment of the packaging, but these means are also still unsatisfactory.